世事艰难，人生不易。 夜深人静时候，回顾过去，往事历历在目。创南京，混苏州，下上海。都付出了巨大的努力。多少个不眠的夜晚，在左思右想。天生愚钝。又不是学计算机的。一直没较为深入的理解node
编程什么东西，一直没有入门。linux
感谢Qisda, 让我在08年就开始接触android. 都不容易。android
编程是什么？编程
编程是数据处理。如何处理？ cpu经过指令指针的跳转，实现了读下一条指令，cpu实现了读指令，编译指令。ubuntu
感谢marvell. 哎marvell技术 不可谓不强。认识一大批牛人。jialin, jiaguo, xinjiang wenzhao fuqiang ruikuang xia . 哎，咱们一个team。我是最菜的。一个上海交大，一个武大，一个哈工大。一个南大。
一个中国科大少年班。南航和他们比太菜了。哎。 就不断的琢磨。学习
仍是老套路把。先从简单字符驱动开始。测试
驱动是为了沟通os和硬件。起到了承上启下的做用。哪就说明这个模块就能让os认识它。有能操做硬件。ui
那如何让os认识它呢？spa
就一句话int cdev_add(struct cdev *p, dev_t dev, unsigned count).
那这些参数哪来的呢？操作系统
struct cdev就须要本身建立结构体内存。 dev_t是分配的设备号。
struct globalmem_dev{
struct cdev cdev;
unsigned char mem[GLOBALMEM_SIZE];
};
这样就建立了这个结构体。初始化时候分配内存就行了。为何要弄个结构体。弄个静态全局变量能够吗？ 也能够的 。可是不太方便。为何不方便呢？ 下面说
还要分配设备号
if (globalmem_major){
result = register_chrdev_region(devno, 2, "globalmem");
}else {
result = alloc_chrdev_region(&devno,0, 2, "globalmem");
globalmem_major = MAJOR(devno);
}
有了cdev dev_t. 就能够添加到os了。
为何参数要有个设备号呢？ 系统有不少的驱动，应用程序只看到设备节点。当应用open的时候，系统会看大这个设备的设备号。根据设备号找对应的驱动。因此add的时候须要跟上设备号。
cdev初始化还要加上fop。
static const struct file_operations globalmem_fops = {
.owner = THIS_MODULE,
.llseek = globalmem_llseek,
.read = globalmem_read,
.write = globalmem_write,
.unlocked_ioctl = globalmem_ioctl,
.open = globalmem_open,
.release = globalmem_release,
};
当应用call open的时候，操做系统会先作一些通用的处理。作什么通用的处理我也不清楚，正在学习，不知道就不知道。千万别像书上写的。这里通常用不到。没必要了解。不了解中国人怎么写出操做系统来？
作通用处理的时候会产生inode file两个结构体。 同时把file的fop的控件用驱动的add的cdev里的fop初始化。哪确定的，否则之后read write时候参数都有file指针，那系统如何找到咱们驱动的真正的read write
实现呢？
static int globalmem_open(struct inode *inode, struct file *filp){
struct globalmem_dev *dev;
dev = container_of(inode->i_cdev, struct globalmem_dev, cdev);
filp->private_data = dev;
printk(KERN_ALERT "globalmem_open!");
return 0;
}
dev = container_of(inode->i_cdev, struct globalmem_dev, cdev);
filp->private_data = dev;
这两句话看清楚了吗？ 使劲理解。
下面把个人测试代码发出来把
#include<linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
//#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/slab.h>
MODULE_AUTHOR("qcom.shanghai@gmail.com");
MODULE_LICENSE("Dual BSD/GPL");
#define GLOBALMEM_SIZE 0X1000
#define MEM_CLEAR 0x1
static int globalmem_major = 0;
struct globalmem_dev{
struct cdev cdev;
unsigned char mem[GLOBALMEM_SIZE];
};
struct globalmem_dev *globalmem_devp;
static int globalmem_open(struct inode *inode, struct file *filp){
struct globalmem_dev *dev;
dev = container_of(inode->i_cdev, struct globalmem_dev, cdev);
filp->private_data = dev;
printk(KERN_ALERT "globalmem_open!");
//marvell 臧春杰
return 0;
}
static int globalmem_release(struct inode *inode, struct file *filp){
printk(KERN_ALERT "globalmem_release!");
return 0;
}
static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos){
unsigned long p = *ppos;
unsigned int count = size;
int ret = 0;
struct globalmem_dev *dev = filp->private_data;
if (p >= GLOBALMEM_SIZE){
return 0;
}
if (count > GLOBALMEM_SIZE - p){
count = GLOBALMEM_SIZE - p;
}
if (copy_to_user(buf, (void *)(dev->mem + p), count)){
ret = - EFAULT;
}else {
*ppos += count;
ret = count;
printk(KERN_ALERT "read %u bytes from %lu \n", count, p);
}
return ret;
}
static ssize_t globalmem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos){
unsigned long p = *ppos;
unsigned int count = size;
//marvell 臧春杰
int ret = 0;
struct globalmem_dev *dev = filp->private_data;
if (p >= GLOBALMEM_SIZE){
return 0;
}
if (count > GLOBALMEM_SIZE - p){
count = GLOBALMEM_SIZE - p;
}
if (copy_from_user(dev->mem + p, buf, count)){
ret = - EFAULT;
}else {
*ppos += count;
ret = count;
printk(KERN_ALERT "write %u bytes from %lu \n", count, p);
}
return ret;
}
static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig){
loff_t ret = 0;
switch(orig){
case 0:
if (offset < 0){
ret = - EFAULT;
break;
}
if ((unsigned int)offset > GLOBALMEM_SIZE){
ret = - EFAULT;
break;
}
filp->f_pos = (unsigned int) offset;
ret = filp->f_pos;
break;
case 1:
if ((filp->f_pos + offset) > GLOBALMEM_SIZE){
ret = - EFAULT;
//marvell 臧春杰
break;
}
if ((filp->f_pos + offset) < 0){
ret = - EFAULT;
break;
}
filp->f_pos += offset;
ret = filp->f_pos;
break;
default:
ret = - EFAULT;
break;
}
return ret;
}
static long globalmem_ioctl(struct file *flip, unsigned int cmd, unsigned long arg){
printk(KERN_ALERT "globalmem_ioctl");
return 10L;
}
static const struct file_operations globalmem_fops = {
.owner = THIS_MODULE,
.llseek = globalmem_llseek,
.read = globalmem_read,
.write = globalmem_write,
.unlocked_ioctl = globalmem_ioctl,
.open = globalmem_open,
.release = globalmem_release,
};
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index){
int err, devno = MKDEV(globalmem_major, index);
cdev_init(&(dev->cdev), &globalmem_fops);
dev->cdev.owner = THIS_MODULE; //marvell 臧春杰
err = cdev_add(&dev->cdev, devno, 1);
if (err){
printk(KERN_ALERT"cdev_add failed!");
}
}
static int __init globalmem_init(void){
int result;
dev_t devno = MKDEV(globalmem_major, 0);
if (globalmem_major){
result = register_chrdev_region(devno, 2, "globalmem");
}else {
result = alloc_chrdev_region(&devno,0, 2, "globalmem");
globalmem_major = MAJOR(devno);
}
printk(KERN_ALERT "major-------------->%d \n", globalmem_major);
if (result < 0){
return result;
}
globalmem_devp = kmalloc(2 * sizeof(struct globalmem_dev), GFP_KERNEL);
if (! globalmem_devp){
result = -ENOMEM;
goto fail_malloc;
}
memset(globalmem_devp, 0, 2 * sizeof(struct globalmem_dev));
globalmem_setup_cdev(&globalmem_devp[0], 0);
//marvell 臧春杰
globalmem_setup_cdev(&globalmem_devp[1], 1);
return 0;
fail_malloc:
//marvell 臧春杰
unregister_chrdev_region(devno, 1);
return result;
}
static void __exit globalmem_exit(void){
cdev_del(&globalmem_devp[0].cdev);
cdev_del(&globalmem_devp[1].cdev);
kfree(globalmem_devp);
unregister_chrdev_region(MKDEV(globalmem_major, 0), 2);
}
module_param(globalmem_major, int, S_IRUGO);
module_init(globalmem_init);
module_exit(globalmem_exit);
这个代码我在ubuntu16.04上编译测试过。
结果以下
[ 443.797578] major-------------->247
[ 593.833449] globalmem_open!
[ 593.833486] write 13 bytes from 0
[ 593.833499] globalmem_release!
[ 620.507565] globalmem_open!
[ 620.507659] read 4096 bytes from 0
[ 620.509053] globalmem_release!
[ 647.025424] globalmem_open!
[ 647.025465] write 16 bytes from 0
[ 647.025475] globalmem_release!
[ 650.531294] globalmem_open!
[ 650.531327] read 4096 bytes from 0
能够直接拷贝，写个makefile编译，后续我再加点自动建立设备节点。就不用本身mknod了。
不吃苦中苦，难为人上人。千万别成王宝强。